A pump is described in Patent Document 1. The pump includes a cylindrical body, a tube coaxially arranged within the cylindrical body, a cylinder communicating with an inner space between the cylindrical body and the tube, a piston arranged within the cylinder, a motor for driving the piston, and a pressure sensor for measuring a pressure of a working liquid filled in the inner space.
In case of pushing out a delivery liquid in the tube, the motor drives the piston to apply a pressure to the working liquid within the inner space. Then, the pressure is applied to the tube via the working liquid. Thus, the delivery liquid within the tube is discharged to the outside of the tube.
Since a liquid is an incompressible fluid, a pressure of the working liquid is in approximately direct proportion to a discharge amount of the delivery liquid from the tube. Therefore, a driving amount of the piston is controlled according to a pressure of the working liquid measured by the pressure sensor, so that a discharge flow rate of the delivery liquid from the tube can be controlled.    Patent Document 1: Japanese Patent Laid-open Publication No. 2007-154767